2-Haloalkylbenzoic acid derivatives are used as building blocks for the synthesis of active pharmaceutical ingredients. For various reasons, it is desirable for the use to have storage-stable compounds which can additionally be prepared and purified in a simple manner. These reasons include, for example, the ensuring of a constant quality, the avoidance of frequent checks on the materials to record the product quality, the avoidance of the necessity of cold storage and/or cold transport, easy transfer to production plants and also simple cleaning of used vessels.
2-Bromomethyl-6-methylbenzoic esters (A1 and A2) are known, for example, from WO 00/64888 (R=iBu (A1)) and WO 00/64876 (R=Me (A2)). These compounds are not storage-stable at room temperature, since they cyclize spontaneously to the lactone (B) and in the process, as is well known, release mutagenic alkyl bromides as a by-product. 
The use of these thermally labile substances on an industrial scale is therefore associated with occupational hygiene risks, difficulties and additional costs.